1. Field of Invention
This invention relates to a semiconductor manufacturing apparatus, methods for processing a surface of a substrate, and methods for monitoring deposition of reaction products.
2. Description of Related Art
The manufacturing of semiconductor devices utilizes plasma etching and various other plasma processes to etch or otherwise process the surface of a semiconductor substrate. For example, anisotropical plasma etching is performed by i) placing a substrate having a film or layer to be etched on a substrate holder in an etching chamber, ii) providing a etching gas atmosphere suitable to etch the film or layer into the chamber, iii) generating plasma in the chamber by supplying electromagnetic energy to the gas atmosphere, iv) applying a bias voltage to the substrate, and v) etching the film or layer by directing active species generated in the plasma onto the surface of the substrate.
The plasma is usually generated using microwaves or radio frequency RF) electromagnetic waves of 13.56 MHz, 27 MHz, 60 MHz, and so on. As a typical discharge method to generate the plasma, ECR Electron Cyclotron Resonance) or ICP (Inductive Coupled Plasma) may be mentioned. High-density plasma can be generated at a low pressure by these methods. The bias voltage is applied to the substrate by supplying RF electromagnetic waves of 400 kHz, 22 MHz, and so on, to the substrate holder, which also acts as an electrode.
In the plasma etching for manufacturing semiconductor devices, improvements in characteristics, such as high dimensional controllability, low microloading effect, high selectivity, and high reproducibility, have been increasingly demanded. Because there are complicated trade-off relationships between the above-mentioned characteristics, however, a stable region in which every demand can be satisfied is extremely small. In addition, such stable region actually changes when a large number of substrates are successively etched in the same chamber for the actual production of semiconductor devices.
Therefore, various parameters of the process should be properly controlled in order to realize stable production of semiconductor devices. For example, Japanese Unexamined Patent Application Publication No. Hei 8-199378 (JP 8-199378) addresses the problem that the bias voltage varies in time. This publication discloses maintaining the bias voltage at a predetermined value by controlling the RF electric power supplied to the substrate holder,
An object of this invention is to provide an apparatus and a method, which are suitable to use in the production of semiconductor devices, to etch or otherwise process a surface of a substrate with improved stability.
Another object of this invention is to provide a method for monitoring deposition of reaction products on the inner wall of a chamber of an etching or other processing apparatus. The monitoring method can be suitably used to control the process.
The inventor has discovered that, in general, instability of interaction between the plasma and the inner wall or a ground electrode within the chamber causes an instability of the process. The plasma interacts with the inner wall or the ground electrode. Therefore, the state of plasma changes when the surface state of the inner wall or the ground electrode is changed, even though the electric power of first electromagnetic waves is maintained at a constant value. As a result, the bias voltage, which is generated by the interaction of second electromagnetic waves with the plasma, changes even though the power of the second electromagnetic waves is maintained at a constant value.
The inventor has also discovered that the change in the interaction can be directly monitored by measuring a ground current flowing from the plasma to the inner wall or the ground electrode, and indirectly monitored by measuring the bias voltage. Controlling the electric power of the first electromagnetic waves used to generate the plasma can compensate the change in the interaction Thereby, a stable process can be realized even though it is difficult to prevent the change of the interactions
An exemplary embodiment of an apparatus according to the invention includes a chamber that contains a gas atmosphere, the chamber including an inner wall; a substrate holder within the chamber that holds the substrate; a plasma source that generates a plasma by supplying first electromagnetic waves with a first electric power to the gas atmosphere; a bias source that generates a bias voltage by supplying second electromagnetic waves with a second electric power to the substrate holder; and a controller. Charged species in the plasma are accelerated by the bias voltage and directed toward the surface of the substrate so that the surface is processed by the accelerated charged species. The controller produces a control signal by monitoring the bias voltage and a ground current that flows from the plasma to the inner wall of the chamber, the control singal is used to control the first electric power.
In some other exemplary embodiments of the apparatus according to the invention, the controller controls the first electric power such that the bias voltage is maintained within a selected range by increasing the first electric power when the bias voltage is higher than a selected upper limit and decreasing the first electric power when the bias voltage is lower than a selected lower limit.
In some other exemplary embodiments of the apparatus according to the invention, the inner wall is situated such that reaction products deposit on the inner wall, the reaction products deposited on the inner wall have an influence on the plasma; and the controller controls the first electric power to compensate the influence of the reaction products deposted on the inner wall. The controller monitors an amount of the reaction products deposted on the inner wall by monitoring the bias voltage; and the controller decreases the first electric power when an increase in the amount of the reaction products is monitored and increases the first electric power when a decrease in the amount of the reaction products is monitored.
An exemplary embodiment of the methods for processing a surface of a substrate according to the invention includes holding the substrate on a substrate holder in a chamber, the chamber including an inner wall; generating a plasma by supplying first electromagnetic waves with a first electric power to a gas atmosphere within the chamber; applying a bias voltage to the substrate by supplying second electromagnetic waves with a second electric power to the substrates holder so that the surface of the substrate is processed by charged species in the plasma accelerated by the bias voltage; monitoring the bias voltage and a ground current that flows from the plasma to the inner wall of the chamber to produce a control signal; and controlling the first electric power using the control signal.
An exemplary embodiment of the methods for processing a surface of a substrate according to the invention includes controlling the first electric power, by increasing the first electric power when the bias voltage is higher than a selected upper limit, and by decreasing the first electric power when the bias voltage is lower than a selected lower limit.
An exemplary embodiment of the methods for processing a surface of a substrate according to the invention includes controlling the first electric power to maintain the bias voltage within a selected range; and when the bias voltage is not maintained within the selected range, controlling the second electric power to maintain the bias voltage within the selected range.
Some exemplary embodiments of the methods for processing a surface of a substrate according to the invention include controlling the first electric power and the second electric power by a) monitoring the bias voltage and a ground current that flows from the plasma to the inner wall; and b) when the bias voltage is outside of a first selected range and the ground current is outside of a second selected range, changing the first electric power.
An exemplary embodiment of the methods for successively processing a plurality of substrates in a chamber includes holding one of the plurality of the substrates on a substrate holder within the chamber, the chamber including an inner wall; generating a plasma by supplying first electromagnetic waves with a first electric power to a gas atmosphere within the chamber; applying a bias voltage to the substrate by supplying second electromagnetic waves with a second electric power to the substrate holder so that the surface of the substrate is processed by charged species in the plasma accelerated by the bias voltage; depositing reaction products on the inner wall of the chamber, the reaction products deposited on the inner wall having an influence on the plasma; monitoring an amount of the reaction products deposited on the inner wall by monitoring the bias voltage; and controlling the first electric power to compensate the influence of the reaction products. The controlling includes decreasing the first electric power when an increase in the amount of the reaction products is monitored, and increasing the first electric power when a decrease in the amount of the reaction products is monitored.
An exemplary embodiment of the methods of monitoring deposition of reaction products on an inner wall of a chamber according to the invention includes generating a plasma by supplying first electromagnetic waves with a first electric power to a gas atmosphere within the chamber, the chamber including an inner wall; depositing reaction products onto the inner wall of the chamber; and measuring a ground current that flows from the plasma to the inner wall of the chamber on which the reaction products are deposited.